This invention relates to a employing an optical grid to monitor and control movement of a device. More particularly, employing a processing unit to implement an improved scheme for sending and processing beams of light within an optical grid and using the output of the processing unit to control piezo movement of a motor is disclosed.
Generally, off-the-shelf optical grids allow high measurement accuracy. As used herein, the phrase “optical grid” represents a linear arrangement of optical elements, where each optical element is located at a precise distance from the previous optical element. These optical elements may include “light sources,” which emit a beam of light, and “light sensors,” which become excited by variations in light and detect whether the beam of light is reflected back. Thus, the light sources and the light sensors work in conjunction to measure a position on the optical grid. Often, the light sources and light sensors are paired in a one-to-one ratio.
Further, some piezo motors offer poor resolution because they are limited by the wavelength of the light beams. In the application of locating a lens quickly and accurately using these piezo motors, location errors smaller than the grid spacing cause discernable focusing problems with a barcode imager. This sensor tolerance, coupled with non-linear movement of the piezo motor, rarely allow even quarter grid positioning of the lens to be achieved.
Generally, the present invention resolves the situations of inaccurate piezo motor location for the purpose of auto-focus imaging in a barcode scanner at a price commensurate with current devices (i.e., without additional hardware or more expensive motors).